Art of shadow screen inspection and method and article related to the same



Aim-J7, l1945. v o. c. HEDIN ART OF' SHADOW SCREEN INSPECTION AND METHOD AND ARTICLE RELATED TO THE SAME Filed D96. 10, 1942 4 Sheets-Sheet l tsar, km wim ART OF SHADOW SCREEN INSPECTION AND METHOD AND ARTICLE RELATED TO THE SAME l Aug.15.1945. l o. c. Hmm 2,381,164'- l y E Y Filed Dec. '10, 1942v 4 Sheet s-Sheet l2 Mozey Aug. 7, 1945..- o. c. HEDIN l ART 0F SHADOW SCREEN INSPECTION AND METHOD AND ARTICLE RELATED vTO THE SAME v Filed Dec. 10, 1942 4 Sheets-Sheet 3 ART OF SHADOW SCREEN INSPECTION AND METHOD AND ARTICLE RELATED TO THE 'SAME Filed Dec. l0, 1942 4 Sheets-$11661'l 4 Patented inig. .7,j1'945 2,381,164 ART oF sHAnow SCREEN msPEo'noN AND METHOD AND SAME.

ARTICLE E ELATED T O THE- scar C. H edin, Cleveland Heights, Ohio, assign` or to AThe Weldon Tool CompaneCleveland, hio,a corporationof Ohio Applicationfnecember 10, 1942, Serial No. 468,551-

I'his inventionrelates to the art of optical inspectionin which light is projected generally across the periphery of a piece to be inspected or checked, in a manner to -form anenlarged'pro' 111e shadow of the objecten a shadow 'screen for. comparison with like vdelineation associated vwith that screen.v

" .For many years ithasfbeen'the invariable practice to .intercept -the light projected gnthe costly one; Where shadow screen by the screen becomp'ared with a the shadow margin could be sultant'from interception of the light byl the opaque lines is a very 'objection-L able occurrence and under certain conditions a the shadow of a cutting tool vis observed in relation to the shadow of the 'pe` riphery of the work during shaping and the'opverator 1s watching the progress of the shadow as it is virtually ground down', 4 it happens that the shadow margin 4disappears inthe opaque or dark line of the drawing. After this occurs grinding may continue until'the shadowl reappears on-the opposite side. oi' the line, in which case'too much grinding may have taken place and the piece may have been ground too small or too large, or

have been spoiled.

These optical inspection machines are also used for inspecting work after it has been taken out vof the grinding or shaping .machine for contourv checking. In this case the work piece is mounted on a Stage'insuch manner. that 'the' light can be.

' passed across its periphery'to obtain an enlarged entirely4 with the use shadow can be lost in the opaque-line.

villumination in those areas. Thus, I

profile shadow, and this enlarged shadow is pro- .iected onto theshadow screeny for comparison WiththeconVentional or dark or opaque line drawing. Injthis instance also the prole of theA In order to overcome the diiliculties above mentioned andy to do away entirely with dark-line drawing, I haveconceived of a method offpreventing 'dark-line interference -by ldoing away of such light-'intercepting opacity. .This conception involves the method stepof increasing the degree of transmission oi light in vthoseareaswhich correspond to thevproille delineation, whereby to provide bright-line prevent :ln-. terruption of light in vthoseareas which ,correspond to the outline of the 'master profile.

Myv invention involves: `A method by which bright-line illumination. is attained or by which interception of light inthe delineation areas is an enlarged drawing or-linemeans o i an opaque linedrawf` ing, thus requiringthat the margin 'of the work shadow castvupon v dark line in which lost." v. The Aloss oftheshadow margins .Within those 1 dark areas re prevented; a new article of manufacture by which this method can be carried out;'V the combination with an optical comparing'machine 'oi' my means for obtaining bright-line illumination; a method l ,or technique for ve accurately making my, ar'- ticle of manufacture;

curately and relatively cheaply duplicatingsuch articles in quantity. There are, therefore, a num- !be'r of important *phases 5to my invention, `all based von the conception-of: increasing the degree of transmission of' light in the areas which coru respond to the prole delineation or of preventing dark-line interference -with light transmis- 'f 'sion'in'those areas. .15 My invention includesv the provision of means by which4 bright-line comparison is always at- --tainable and ground glass of an optical comparingmachine.

the ordinary shadow screen or such a machine.

'I'he practice of my invention not onlymakes for much greater accuracy in comparing, but reduces eye strain to a minimum. 'Ihe practice of the invention can also compensate in some degree 'y for a lessened visual acuity of a user. With the on, but to provide a method .o f making master f plates 'by using a .coating of transparent or translucent emulsion on a piece of glass of goodtransparencyv and cutting away'the emulsion to restore l 49 lfull transparency of .the glass in those areas which correspond to the line delineation or proille drawing ofthe part. A feature of the in- .vention is therefore the process or method for cutting emulsion for my purpose.

Other features -include the method of reproduction of a cut plate by a photo-printing process; the production f plates in accordance with myinvention and by a photo-optical method in "which an opaque line drawing is involved; the production oi' an article of my invention by a photo-printing process in which an apaque line drawing Aori transparent or translucent paper or linen is involved: and all method details and `deandmethods for very vacalso lprovides means which 'may be substituted for the ordinary shadow screen vor My article also .can be used in conjunction with ground glass of tails of construction disclosed herein, along with the tool point to the plate or screen or drawing made in accordance with the teachings of this invention;

.Figure 2 is a cross-section taken on of Figure 1; Figure 3 is a View illustrating one of the exposure steps of my method in accurately reproducing duplicate copies of the master plate of Figure 1 by a photo-printing process;

.Figure 4 is a face view of the negative resultant from the exposure step of Figure 3;

Figure 5 illustrates the final exposure step of this method, using the negative of Figure 4;

Figure 6 is a face View of the nal product resultant from the photographic development of the exposed negative of Figure 5;

Figure I is a cross-section on line ure 6; l

Figure 8 is a face view of an article of manufacture produced by applying Aa coating like that of Figure 2 directly to a piece and then cuttingthe coating;

Figure 9 is a section on line 9-9 of Figure 10 is an enlarged view showing the method removing the coating material of the plate to produce the article of Figure 1;

Figure 11 is a plan section on line ll-II of Figure 10 showing the relation of the facets of direction of movement of the tool during cutting; f

Figure 12 is an enlarged .end view looking at the point of the tool;

Figure. 13 is a. perspective View showing a structure which may be used to mount and guide the tool during its cutting movements;

Figure 14 is a face view of a master profile plate from which may be produced by a single optical photographic procedure, an article like that of Figure 6;

Figure 15 is a section on ure 14;

line 2--2 1--1 of Figline I5-l5 of Fig- In those figures of the drawings which relate I to my products and to the processes related thereto, the` showings are somewhat diagrammatic; thicknesses are devices are` resorted to exaggerated and other for clarity of conception,

' rather than to achieve proportional accuracy.

of ground glass j Figure 8;

The numeral I indicates a glass plate of good light-transmitting quality. Numeral 2 indicates a coating of suitable density on the plate.- I'he application of this coating reduces the lighttransmitting properties to the proper degree to aord optimum contrast with clear transparent areas, and/or to permit of light transmission for e. photo-printing process. The numeral 3 indicates line-like areas in which the coating has been removed down to the glass in a manner to restore full bright-line transparency to the glass and to delineate a, master proiile drawing. Accurate duplicates of the article of Figures 1 and 2 can be made by line-like removal of the coating, and very accurate exact duplicates can be made from this cut master plate by a simple photo-printing process herebelow described and constituting an important feature of my invention,

Various materials 'may be used for coating the plate to provide a homogeneous light-transmitting film or layer of uniform thickness and optical density which can be cut through to .the glass and cleanly removed, and which has the proper degree of light-transmitting ability whereby to permit observation of a sharp line shadow of a shadow screen. The degree of light transtransparency or to translucency, depending on the specic uses to which the final product is to be put and upon the method of reproduction used in making duplicate plates.

A coating material which is useful and which A can be properly cut is composed of a suspension Figure 16 is a diagram illustrating one stepproduct like Figure 18 is a face View of an article from\ which a final product like that of Figure 6 can be produced by a photographic Figure 19 isa section on line 18;

Figure 2d is a diagram showing the exposure step in the photographic printing of the article of Figures 18 and 19;

Figure 21 is `a. cross-section of the final product resultant from photographic. development of the exposed negative of Figure 20; and

Figure 22' is a view illustrating my method step and the combination of my master plate with the ground glass of a comparing machine in carrying out that step.

Referring first to Figures l and 2 which show a master profile drawing plate m'ade in accordance with the teaching of this invention.- The plate shown represents the preferred embodiment of this invention because it can be very accurately made and veryvaccurately reproduced or duplicated by a'- simple photo-printing process.

printing process;

l9`l8 of Figure of small particles of metallic silver in gelatin, treated so as to be particularly adaptable' to clean line removal by a suitable cutting tool. This coating may be colored; it has a small coefficient of expansion, and is suiiiciently hard to be permanent in storage and handling.

The degree oftransparency of the coatingor emulsion is important but is variable. Ordinarily the final product of this invention should be suiciently transparent topermit one to see the outline of objectsby looking through the plate after application thereto of the emulsion. After 1 cutting and removing the emulsion down to the glass, line-like areas of clear transparency result and these areas are contrastedly related to an area of lesser transparency. In other words, both areas will transmit .light for photographic printing and the larger area which is not cut will be suitable for the observation of a sharp shadow created by transmitted light.

When laid against the ground glass' screen of a comparing machine, the light-transmitting quality of my plate is such that after passage of the light through and diffusion within that screen ,and through the plate, a clean-cut shadow is easily visible for comparison with the bright-line delineation of the plate.

I do not intend, however, to be entirely limited to theuse of a transparent coating, because I may' wish #to provide-a plate which :acts y'as a gruzmdgla'ssin Vlieu `oit-the' ground glass or the ordinary comparing in which. case :the coating williibe translucent or. will be: rendered traslcent by aphoto'graphic .procedure a'sheremattermentioned. A g

jfThe-'characterofthe glass should be such that thosefareasrwhichcorrespond 'to the masteriline vvzlelinezattion.can be highly transparent to givea bright-line visual; appearance during the'inspection period and the remaining emulsion shouldbe just'sumciently denser tov allow the observation ora-sharp shadowtwhich can.' be comparedxto and orientedawith thebright-line areas, Whatever the color or lightetransmitting quality is, it shouldfbe-proper for/the'purposes above... It will,` therefore, vbe `seen that *ilrstv and foremost' this invention provides a bright-line-appearance in those areas. :winch correspond to the linedelina cation, y"whether obtained. by cutting away the emulsion or coating, or `by photo-printmg or' by photo-optical methods.. The .remaining area oiy the 'coating is suiiiciently light-transmissive to observation .of yor to givefa;V shadow of .the needed sharpness fzorcomparison withthe brighwl line delineation. f

. I yhave referred to one kind of coating material whichJI'jhayefxfound :to be useful and which is composed oiga suspension 'of small. particleszof, silver-.1in av'suitable-- or gelann. l am not :concerned with the manufacture:- of thematerial, :nor .with the application of such material f toa glass plate. Manufacturers of the "photolgraphic lms and coatings and emulsions are skilledinsuchmatters as precipitation of silver vl v from silver `salts and inmethods of ,dispersing such nely divided silver'particles evenly ina suitablecarrying medium and obtaining the propter (proportion of all ingredients. The filmv or coating which I use is 'not .light-sensitive in a f photographic sense,v but the material. of the coatingymay .be madeby suitahly'modiiying emul` sionmaking materials. Thus, .the 4degree-'ofl lightetran'smitting ability and the degreeI of hardness ofthe coating can be varied: as is required. NolimitationI isintended by mentioning the productionuof my covering material by theuse of metalhccilver 1in gelatin. Other materialscan .and should beof even thicknessvthroughout. It isvfsuflicientiy hard to. allow the-use of .the scribform line-width 1 cutting and. yremoval of thematerial'.I f'

When` Iuse the expressions .fmaster drawing and article Yof manufacture I. mean an article inswhichthe line ldelineation is and must befen with the shadow screen of such a machine. My

- belusedjor my purpose. The nlm. is quite thin ingftool described herein toobtan clean, uni# article requires the greatestaccuracy in its production, as `will be evident fromthe description hereinqrelating tothe vmachine by which the ,drawing is accomplished.

. .Giass plates having a coating .which is suitable for cuttinabymy process herein for'the production vofniy article. of manufacture; andkk having the reqInredlight-transmitting properties arel obtainable underthe trade-name Kodak Scriber yPlates,manufactured by the Eastman Kodak Company.

, `Although Figures. '7, 1'7` and 21 are sectional views yety no sectionlining lhas rbeen kused `in those areas which. correspondrto the delineation.

This has been resorted to to indicate thatinmy finished article all." line-like -areas are brightly transparent,` and` that there is great contrast between these line-like areas and the remaining denser or tinted. area of the coating. In all views where delineation. has been represented., linewidth has Abeen exaggerated.4 yOf course, 'what may be designated as wide-line. delineation may bewsorted. to, `or double-.line delineation may be used.: Ali canbe obtained by cutting suitable covering material.

The articlefof vFigure/1 can be. ofany suitable size and any required or desired characterv of master delineation may be made and duplicates can be made. to have a high degree of visual qual# ity. lAs to the production of duplicates by cutting,'this can' be. very accurately done by the use of a devicedisclosed inmy copending application for Drawing machine or rial Number459,l02.

Master plates ofl standard commonly used proles such as screw thread profiles,` gear tooth prunes,4 mastervangles, master radii, etc., maybe produced by this line-like removal ofthe coating material. to obtain maximum transparency in the cut-area. Clean lines of uniform. width varying from .006 vinch to..0(l3.` inch can "be cut by my method and means, and much greater accuracy as to line-width uniformityv and profile dimension can be achieved by cutting as herein disclosed than bythe use of lead'pencil orink lines asis usual in makingprofile master drawings.

Before describingmy' preferred methodancl means "for cutting lthe emulsiony or coating'to produce the. product ofFigures l andiZ, I will describe my process for obtaining accurate. duplicates from said product. it will be understood, ofcourse, that thearticle of Figures 1 and A2 can .thatthere are no cut lines. in the former. In

the brightly transparent line-like `areas of my plate fofv `the photo-printing method the light passes through. a very transparent portion of the developed photographicv emulsion. It will'be. unlerstood` that thisA is' the preferred manner of duplication, since I have found it. to lbe the most accurate; The process involves a=simp1eph0t0- printing' orcontact-printing process, falong with the'. development .of exposed photographic plates, inthis case involving the exposure and develop tuenty of two plates. A glass plate is preferable fromthe standpoint of dimensional stability in relation to changingtemperatures and humide tothe use of a glass'basenor'to a stiff base..

e' Now, referring to Figures 3 to 7, inclusive. To obtain accurate .reproduction of the article of' liguresi` l andl 2, its. emulsion or cut face is placed as in 'Figure 3 against the facev of the emulsion' of asuitable photographic plate 6. Light is 'then passed through in the direction of the arrowLA, anda proper degree of `exposure-is given. yAfter development of the photographic plate-6` a negative is produced and is designated byinumeral "Lsee :Figure 4. .The opaque line k3 of this negative is lof exactly thetsame width as thai-...ofthe width of the cut out area3 of the article of Figures l and `2.l The emulsion side of the.y negative 'lV is ,then placed` as in Figure 5 1ay-out table, Se-

iti'es. Yet. I do not.y intend to be entirely limited A against the emulsion side I of a second photographic plate I I, and light is passed'through the plate as shown by the arrow B. After development of the plate II-the article I2 of Figures 6 and '7 is produced and the line I3 is forall prac-l tical purposes the exact duplicate in accuracy and light-transmitting quality as that of the article of Figures 1 and 2 and has the bright-line delineation areas which, however, are not cut areas as in Figures 1 and 2.v Both original and duplicate are capable of giving bright-line and easy shadow observation under the conditions o their use.

As made at present, the article of Figure 1 is transparent and has a very thin coating which has a faint brownish tint as viewed by transmitted light; the developed negative shown in Figure 4 is substantially less transparent than the article of Figure 1, and the nal article oi Figures 6 and '7 is less transparent than the article of Figure 1 but is considerably more transparent than the article of Figure 4, and has a grayish tint as viewed by transmitted light. No limitation is intended by this statement. I have only describedthe appearance of one of my articles as it actually is. In the drawing stippling has been used to differentiate the light-transmitting quality of the plates of Figures 1, 4 and 6, but no limitation is intended, and this convention is not necessarily meant to represent a ground glass quality, although my screens or plates may have a shadow-giving quality comparable to ground glass. The fcolor or lighttransmitting quality of the coatings mayv be varied to suit use requirements. The glass has excellent light-transmitting quality and has the thickness of an ordinary Aglass photographic plate. Of course, the invention is not limited to the use of a stiff backing nor to the use of glass, yet glass is the most practicable material and stiffness is most desirable for my present use.

My invention is usefulunder any conditions wherein accurate comparison or registration is required between a shadow and a line so that I do not consider this invention entirely limited only to use with `optical inspection machines and to tool shadow comparisons.

Now it may be desirable to produce an article of manufacture which can be placed in the frame of an optical comparing machine and/,or be substituted for the usual shadow screen or ground glass of such a machine. In this ca`se a cutemulsion master plate or a duplicate of the same made by the above process can be used and it can be of circular shape as shown in Figure `8. The article of Figures 8 and 9 is like that of Figures 1 and 2. Bothare produced by cutting and removal of emulsion or `other suitable material. In this case the ground glass surface I6 of a circular piece of glass I is coated with a suitable material I'I, as previously described, and then the 'master delineation is made by cuttingI and removal of the material down -to the ground surface of the glass, as'shown at 3. Figure 9 shows a cross-section yon line 9-9 of Figure 8.

The previously described photo-printing method is used for reproducing the article of Figures 8 and 9, just as it was used for reproducing the article of Figures l and 2. The only difference is that this article can be substituted for the ordinary ground glass, instead of being attached to the ordinary ground glass or shadow screen. This is a valuable feature of the invention.

In cutting the emulsion as placed on the ground glass side of apiece of ground glass, care is exercised :to make the cutA while-applying an optimum amount of axial pressure tothe cutting tool so as tov accomplish clean line removal without adversely` marring the ground glass surface.

It will be understood that gradations inlighttransmitting quality of Ithe articles of 4my invention when the same are made by a process involving photography, can be obtained by-varying the time of exposure, and this is true for photoprinting ask well as for photographic optical methods. f

Now referring to the process of making the article oi Figures 1 and 2. Referring to Figures 10, 11, 12 and 13. By experiment I have found that the manner of shaping the tool and themanner lof its use are important in the production of the emulsion-cut article of Figures 1 and 2, and these procedures are features of this invention.

To make the master profile delineation by cutting away emulsion or other suitable coating material, the formation or shape of the point of the tool the rapid motion of the tool 'and the proper placing of the facets of the tool in relation to the direction of motion of' the tool are important factors in getting clean-cut and uniform removal of the material.

In Figure-l3 I have illustratedone form of holder which is usable for my cutting tool, a similar construction having also been shown in my copending application 'Serial No. 459,102 for Drawing machine'or lay-out table. It will be understood that the tool must be rigidly held in a certain position while in contact with the emulsion during cutting.

The numeral indicates a suitable base or bar upon which is mounted a saddle 2I having a longitudinal groove 22 in which a scale 23 is xed. The longitudinal sides of the saddle have V-shaped ways 24. The scale is provided with a slide 25 movable along ythe ways, and this slide carries a Vernier 26 cooperable with thescale. This slide 25 lcarries my cutting instrument or scriber. Means is provided so that the tool can be translated .tononoperative position or can be removed, so that another scriber can be sub- Stituted. A suitable weight or weights (not shown) are provided to press the tool with the proper degree of force against the emulsion to be out, and to hold the tool in such operative CII position during cutting.

The scriber-supporting means includes a tubular bushing 28 which fits in and extends through an opening 29m an arm 39 of the slide. A scriber body or holder 3| is slidable and rotate able in the bushing 23 and at its lower end has a suitable chuck 32 which securely holds the scriber 33. In Figures 10, l1 and 12 the scriber has been considerably enlarged to more clearly show the structure of its point. I use a short carbide -tip or other very hard material which is about one-sixteenth of an inch in diameter or larger. The height of the pyramid is about equal to the diameter of the tool.

The upper end of the bushing 28 is provided with two axially extending slots35, 31 which are spaced apart and also has a relatively shallow slot 38vwhich is located between the two slots 35, 31. The body orholder 3| carries a radialY pin dfwhich when engaged in the shallow slot 38 holds the body in a relatively elevated inoperative position so thatthe Itool will not contact the emulsion. When thevpin is moved into lone or the other of slots 35, 3l, the point will engage the emulsion for cutting. A weight (not shown) is applied on theupper end of the scriber body placement.A iszobtained..

'. The slots '335.1 andA 3.1 `provide means whereby the y toolcfacet. can i-always bef'brought .to this` position 4 preparatorytoicuttinglhescriber assembly is heldagainstzaccidental withdrawal by va fork. 50

una' clampingbar 5i, said fork receiving the holderrand-engaging against/a;collar lil.v The fork .is broughtint-o; clamping engagement.- with the collar by first movingthe bar longitudinally and this is accomplished. by means. ofthe slot. 53 andheaded pin 54. For clampingtl'ieV end ofthe bar 5ft is lifted Icy-means of fthe thumb-screw 56- and lifting action causesfthe-fbar to fulcrumon'the; pin 54, thereby. pressingy the `fork against the collar.. When the scriberf holder;v is toV be removed rtl-1e. thumb screvirv isrotated;v in the opposite direction to :relessetheclampingipressure of; the fork on' the collarxand then the bar. is translated'. to withdraw thelfork tofapositionlaterally ofthe collar..

Means 51 torrclampingtheslide 5y is. provided and then bar is moved in a direction perpendicularl to; its long dimension for `cutting purposes,- al-l inthe manner: set forth lin myy application `be.- foregreferredizto.; e

, Oftcourse, anysuitable: mean-sacanbef used for v -holding'thetool and for'rmly holding` it With one of" its..V facets faced. in the direction of vmovement and at right angles to that direction. The struc@ tures of Figu-re-.-l3.sho-Wsy one.: means for positively holdingfthetoolso that my'cutting processcan becarriedout:

Figures. V1.0I and` lil. showthe, tool in. the. act; of cutting througlrtheemulsion. In Figure l1 dotted lines,- show. the division-s between .the facets of. the triangular pyi-'amidall point. The arrow vC of Figure 16` showsgthe `direction. of the cut 3' and showspart. ci the-outras completed., Figure.. 10 shows: the relation of: the pointv to the;,emulsion tationfintended i by this. statement.

' ple photographic procedure which includes aI and torthe'surface of thev glasszplate. Eigure12 f isfa view. looking aty thepoint after it, hasbeen turned through anarc. c1180? fronrits. position in.fltiiepira11.1V L v Thevvidthof `thescribed orA cut line. maybe varied by varying the character of the pyramidal point. A fine line is best.: Itssxwi'dthmay-'range from .003:*i-ncl1 to .006 inch.v To get a ne. line the tool should ..be.ground..to the finest possible point and thematerial of the tool should be; hard enough toresistgwear, since it comesA in sliding contact with glass'. Itxshouldnot be, sobrittle: astof be weak.when..formed intoadelicate and accurate point. Ahardsteelor carbide tool practifcable., butindustrialgdiamond. may be. used;` The, pointzoi'.y the; tool-'should be exactly Ion the longL axisotthe. cyiindrical body so that Whatevery facet'l iafaced in direction of the cut, thev pointv will occupy the same position in relation to othery parts of the' machine by. which the movement Iof the tool is being controlled. This has to do With drawing accuracy.

I'he Width of thebright-line area as made by the. use of my invention can be predetermined and made to. conformwith the gauging ortolerance limitsr ofthe. Workpieceyin question so that the shadow will fall Within a. transparent and brightly illuminated area. The finerv theline the closer and vmore accurately can the comparison be made. Uniformity of', line: Widthis importantl and my cutting methodresults in `greateruniiormity of linewidth Athan is possible when opaque material suchas that of. aleadpencil or, such as ink is used.

- After` production oi` aV master plate by cutting to. f provide the ztransparent line profile, the. cut surface may be: protected from marring and from linger.marks4 incident to handling and storage by means of a suitable transparent. lacquer which may be applied .with ak brush. There-after, finger marks; may be removed from the lacquer by using a pledget of cotton which" has been tnoistened in a soap and Water solution..

The plates. may Vary in size from 4. x 5 inches up to 14 x 17 inches. There is, of course, no limi- It is made merelytoshovry that various sizesofmaster plates may be made by cutting.-

- Whil'eI believe that-the most accurate way to producel and duplicate myv article i's by the methoclspreviously described,` yet I have found that duplicate profile drawingr plates can be made from a master plate which has -a drawing' thereon made with opaquelines. Reproduction from such an opaque line drawing can be made either by a simphotograplgiiol lens; or by a simple-1photo-painting process as previously describedl except that the exposure-of only one negativeandv its development isnecessary.

I believe thatno photographic scheme of reproduction by the use of a lens is as satisfactory in every respect asv that of my piloto-printingv process, as related to my cut-emulsion plate. I do not believe that as accurate line-Width uniformity canbe obtained by opaque line drawing as is obtained by-my scheme of emulsion-cutting.. Yet I have disc-cvered a method oi making a product somewhat like 'that f of Figures 6- and?` by the use of a'copy camera. This method involves the use of opaque line delineationof the master profile drawing on opaquepaper or other suitable opaque medium. From this aproductl having the brightrline and other visual qualities of the cut plate of my rinvention is produceable. Iv therefore de-l scribe andclaim this process `by which a brightline delineation plate results. Since I have found Ways-or methods ofv making a bright-line delineation plate other thanbyf'cutting the emulsion., I consider thenoW-to-be-described methods to be related Atothe broader aspectsof myr invention.

Referring first to' Figures 14 and 15. The numeralf 6U indicatesv a` glassplate of good transparency, to theface of'which has been suitably attached apiece of` opaque paper indicated at 6l. Here-We have'anr opaque layerv on a trans'- parent base. ThisV paper ispreferably of gray shadei Whenthe; paper of this color isY photog-raphedwitli' thev proper timeexposure, the resultant negative* after development gives a suiii'- cientlytransparenter suiiiciently translucent background for the purposel herein. Any suitable shade ofo'paper or any'degree of photographic exis a diagram. The surface of the article of Figure 14 is pla-ced at the proper distance from the lens 64 of the camera B5, and a suitable photographic plate 6B in the camera is spaced an equal distance from the lens at the opposite side thereof. A suitable time exposure is made and then the plate 66 is developed, to produce the article shown in Figure 1'7, which has a transparent base indicated at 61 with a transparent or translucent area indicated at B8' providing therein brightline areas indicated at 69. This article of Figure 17 has the desirable quality of bright-line transparency and the method of producing it is considered a valuable feature of this invention. While a one to one distance ratio has been above mentioned, there is no intention to be limited entirely to that ratio.

I have found a second method involving the use of opaque line drawing from which I can produce the article of my invention. This can be accomplished by a simple photoprinting process. Referring to Figures 18 and 19. In this case I attach a piece of transparent paper 10, such as tracing linen, to a piece of glass 'H of good transparency. Here we have a transparent base and a transparent or translucent layer. On this tracing linen or equivalent transparent material I make an opaque line drawing indicated at 12, using either ink or pencil. The article of Figure 19 is then placed against the emulsion side 'M of n the photographic plate indicated at 15, as shown in Figure 20. A photographic exposure is made with the light passing in the direction indicated by the arrow F. The plate 'l5 is now developed in the usual manner to produce the article shown in Figure 21 and generally indicated by the numeral 1B; This article provides a bright line area indicated at 11 and as to general visual characteristics is substantially the same as the article in Figures 6 and 7. A modification of my invention involves the substitution for theplate I l of Figure 5 of a piece of ground 'glass having its ground glass face coated with a suitable photographic emulsion. The coating of the article of Figure i is laid against the photographic coating of the ground glass plate, and exposure to light for theproper length of time is made, The time of exposure is such that after development the surface coatingl will be of sufficient transparency to exhibit to an observer a shadow which may have been cast upon the ground glass.

In Figure 22 I have illustrated my broad invention herein involving the method step of increasing the transmission of light in those areas which correspond to the lines of the profile delineation, `that is, preventing interception of light in those area. In this drawing increased transmission or prevention of interception of light has been accomplished by placing my article of manufacture in operative relation to the shadow screen of a comparing machine. The view is diagrammatic. The numeral 80 indicates a light source, 8| a piece of work, a shadow of which is to be projected. Numeral 82 represents a suitable optical system by which the shadow of piece 8l is enlarged and projected onto mirror 83. In this instance my plate, either a cut plate shown in `Figure 1 or the reproduction shown in Figures 6 and '7, has its emulsion side 2 laid against the ground surface 84 of the shadow screen 85. The light is reiiected from a mirror 83 through the assembly, while the assembly is .viewed by an observer positioned at `86. This combination -with a ground glass, of my plate having brightline areas 3 is believed to be new, as well as my method, and therefore my plate is also claimed in this combination. When my article is used its emulsion surface should be in contact with the surface' of the screen .to avoid adverse refractive and parallax effects.

It is to be understood that by the practice of my invention, plates having varying degrees of light transmitting quality can be produced for use as shadow screens per se, or for use with shadow screens of standard contour comparing machines. It will be further understood that in the processes of photographic or photo-printing reproduction, various amounts of exposure to light may be resorted to and that various proper shades and colors of covering material may be used on the glass base of good transparency.

For years the master profile delineations of plates adapted for the use herein have always been opaque, so that the shadow outline would become lost in this opaque line, resulting in less accurate comparison work and in overshooting, which overshooting corresponds to overcutting or grinding of the metal piece being shaped. By the practice of this invention such brilliant contrasts are obtained that much more accuracy is obtainable'.

It will be understood that gradations in lighttransmitting quality of the articles of my invention, when the same are made by a process involving photography, can be obtained by varying the time of exposure, and this is true for photoprinting as well as for photographic optical methods.

In ordinary optical inspection devices the light crosses the periphery of the work piece to produce a shadow which is then magnified and projected onto the screen. In this case light is intercepted, due to the opacity of the work piece. By the use of my bright-line delineationk method a face of the object can be illuminated so that the object can be seen on the screen by light reflected from that face or surface. Thus, surfacestructure or finish may be seen on the screen or ythe size and shape of a recess or depression which may not extend through the piece may be so seen. In this method of projecting and viewing by reflected, instead of by transmitted, light my brightline delineation method also has obvious advantages.

I claim as my invention:

A chart or master drawing adapted for use with the screen of an optical inspection machine comprising, a substantially transparent base material'having thereon a material providing aV eld adapted to visualize a shadow, portions of said field material being modified to provide line delineations made to scale and representative of an enlarged scale drawing of the profile of an article to be inspected, which modified portions are substantially more transparent to the passage of light .than is the shadow-receiving material of said field. f

i OSCAR C. I-IEDIN. 

